Time-base circuit for magnetic beam deflection



May 12, 1964 E. J. GLAISHER I TIME-BASE CIRCUIT FOR MAGNETIC BEAM DEFLECTION Filed Aug. 22, 1960 [PRIOR ART gooboooooowq EHT AAAA

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INVENTOR EDWARD J. GLAISHER BY M 12.

AGENT United States. Patent 1 3,133,228 TIME-BASE CIRCUIT FOR MAGNETIC BEAM -1 DEFLECTISN Edward JamesGlaisher, Hurley, England, assignor to 'North American PhilipsCompany, Inc, New York, p N.Y., a corporation of Delaware I a Filed Aug. 22, 1960, Ser. No. 51,199

Claims priority, application Great Britain Sept. 2, 1%9 9 Claims. (Cl. 315-27) V1'=1ine output valve V2=booster diode V3=' EHT rectifier Cb =boost condenser V Rg2=screen grid resistor Ld=deflection coils To obtain a linear scan with a picture tube having a substantially flat screen the circuit must compensate for the changes in the length of the path of the electron beam when traversing the tube face. This requires an expansion ofthe center portion of the line scan with respect to the ends. Some compensation may be obtained by a suitable choice of the boost condenser Cb. However, for large-deflection angles this method of compensation produces'unsatisfactory valve operating conditions and it is customary in this case to obtain the compensation by inserting a capacitor in series with the line deflection coils. The circuit should be designed so that the required deflection is obtained under conditions which will give an adequate expectation of life to the line output valve VI. A common cause of failure of this valve is the inability to supply the required peak anode current after a long period of use, and hence limitations are imposedfon the design'of the equipment to ensure that the valve is work- 'ing well inside its rated capabilities. The design limits .of peak anode current depend on the screen voltage and hence on resistance .RgZ' and'the HT supply voltage. .:Since the peak' anodecurrent occurs 'at the end of the .scanningperiod, the "screen grid voltage at the end of jscan. must be adequate. This voltage may be increased 1 by a reduction of the value of RgZ but a limit is reached When the screen grid power dissipation becomes excessive.e Y i According to the present invention a line time-base circuit for 'magnetic deflection comprises deflection coils i connected by wayof a capacitor across a winding formf ing' part of .an'output transformer which is connected to. a .multi-grid 'output valve having theusual control'igrid V 7 i and a screengrid and adapted to produce a-sawtoothjcuritor'g' said capacitor-having avalue such that, in opera of the line scan than at the center portion thereofr t fiilgthof; the beampath-so as to give bette a linearity." v V v made to flow through the deflection coilsthuscausing a by the anode'current o {rent insaid deflector coils, and means for applying to the du es e t j screen grid of said-- valvea direct voltage-in combination '1 j with-an alternatingvoltage developed across said cap'action the screengrid supplyvoltage is'higherat theends In such a circuit the-capacitor includedin thedefleC- gtion coil! circuit may be used'to correct for changes. in

H 7 C mp r n t e circ .As will be explained, the screen grid current ca n be fdenser Cb has been repositione'd so as to ac as an AC.

3,133,228 Patented May 12, 1964 "ice , 2 small steady displacement of the picture, and this can be advantageous in the case of a television receiver of the directly-synchronized type. In such receivers a steady displacement is often applied by permanent magnets so as to centralize the picture on the screen, but these shift magnets are liable to cause distortion of the raster and interfere with the focusing of the beam. They are also apt to cause so -called corner-cutting or corner shading in tubes employing 110 deflection angles, i.e. they 10 are apt to cause the beam to strike the envelope at the junction between the neck and the cone at maximum deflection. 7

The reason for thisshift requirement (which is likely to be common in 110 directly-synchronized receivers) is that the conventional110 tube aspect ratio of 5 to 4 requires an overscan in the line directionto give the correct proportions to a4 to 3 transmitted picture. Hence the ends of the line scan do not appear on the tube face. Advantage is taken of this by increasing the line flyback time until the left vhand edge. of the picture becomes folded over, thus leasing valve operating conditions. When this is done however, the picture content is displaced with respect to. the raster (since the line flyback cannot start until afteruthe start of the line synchronizing pulseon a directly synchronized receiver) and by the use of D.C. in the line deflection coils the picture can be centered on the screen with the aid of smaller centering magnets which cause less raster and spot distortion and less shading in the corners of theipicture. As will be appreciated, sincethe coils are designed to provide a deflection field which is substantiallyuniform, the resulting centralizing shift of the raster is obtained with little or no adverse effect on the raster shape and spot size. If

the flyback is made to continue beyond the end of the backporch of the transmitted waveform in accordance with afknown techniquejrequiring blanking of the first part of the video signal, the need for a steady shift is correspondingly accentuated.

In a preferred arrangementthe transformer is an autotransformer havinga first and a second Winding wound on a common core and connected in series with. each other betweenthe aforesaid capacitor and the anode of the valve which windings are connected to each other through a capacitive A.C. connec tion,' and the circuit'in- 4 cludes a rectifier connecteda's an efficiency diode between fa D.C. supplyterrriinal and the auto-transformer winding nearest to the anode of said valve, means for'applyingto the screen grid an AC. voltage appearingat the'junction between said capacitorand auto transformer, and means for connecting-thedeflectioncoils across {the series' flcombination of said caplacitorand the adjacent winding;

. In arrangement'itr is prefenableifor the screen grid to be 'conne1cted, jrhhrough a; screen grid. resistance to the junction between said oapacirtorland the lanpo 'qransfommer.

' This has. the advantage of causing (th 'e DC. screen-grid current to mhroufgh the deflecflon 'poilslasaforesaid. Lin addition, the[D.C.-, screen-grid current isf herebymade irto flopw rthmough the part of" the line (transformer supplying v "the" deflection ,coilsin such manner to produce a flux iin t e t s e mrem oppo it o t t t, p ce e1lineoutput valveg 'l his re- A ux mt 'e hai s m: we; iv a j re ion Q SiQSJ nd d ed ma n i jiA pecific m od me t f t t ent mlh yi fl aforementioned preferred tfeatqres vil-l now. be described by'gway ofexample reference to'F-IGUKES .2 and 3 in WO Pauy n-s drawin im e i e m' hasecirouit employing 'a vacuum pentode vial-ve for use lwith 9 a t te evis oi d claims sw tconnection between the that and second windings of the auto-transformer but this in itself has no eftect on the operation. A capacitor Cs is included in the deflection coil'circuit to give the required scan linearity and is so positioned that the voltage at point A has a line-frequency alternating voltage of the term shown in FIGURE 3 (this alternating voltage is produced by the sawtooth current flowing in capacitor Cs). I

The screen-grid resistorRgZ is connected to point A so that the screen-grid supply voltage is increased at the end of a line scan but decreased in the middle of a line scan. This allows a higher voltage on screen-grid g2 at the end of scan .without any increase in screen power dissipation, and hence permits the valve to supply larger scanning currents.

If desired, a capacitor CgZ- may be connected in parallel with the resistor Rg2, to ensure that the alternating voltage as shown in FIGURE 3 is not attenuated, re-I sistor Rg2 should be large. pacitor cgz can be omitted.- p

A practical set of values and components suitable for V the circuit of FIGURE 2 as applied to the British system is given byway of illustration in the following table:

I With the above values the line-frequency alternating -If resistor Rg2 is small, ca

ing a current having a sawtooth-shaped waveform through said winding means, a capacitor, means connecting said deflection coil means and capacitor in parallel with a portion of said winding means whereby a voltage having a direct component and a second component thatvaries with variations in said current appears across said capacitor, and means for apply-in g at least a portion of said direct component and second component or voltage tosaid screen gnid whereby the voltage at said screen grid is higher at the ends of line scan of saidreceiver than at the center of said line scan. a

3. A line deflection circuit for a television receiver comprising deflection coil means, an auto transformer having first andsecond inductively coupled windings, first capacitor means connected between one end of said second windingand a point of constant potential, second capacitor means connected between the other end or said second Winding and an end of said first windingpa multigrid output electron discharge device having at least a screen grid and an anode, means connecting said deflection coil means in parallel with said first capacitor means and second winding, means (for connecting said anode to said first'winding for producing a current having a sawtooth-shaped waveform said deflection coil means,

whereby a voltage having a direct component and a secoridcomponent that varies with variations in said current appears at the junction of said first capacitor means and second winding, and means for connecting said screen grid voltage obtained at point A has'a value of about 'v.

peak-to-peak. This receiver uses relatively low impedance deflection coils (2.7 rnh.) and hence capacitor Cs is required to have a large value for 110 scanning. For receivers using higher impedance deflection coils a smaller capacitance value would be required givinga larger alternating voltage and hence more benefit to the screengrid supply. voltage, If the deflection coil impedanceis too high, the screen-grid loading on the transformer may i become appreciable.

to said junction whereby at least a portion of said direct I and second components of voltage appear at said screen,

gridiand all of the screen \grid current of said device flows in said deflection coil means.

4. The circuit of claim 3, comprising diode means 7 having a cathode connected to said first Winding and an anodeconnected to said point of constant potential.

5.The circuit of claim 3, wherein said means for connecting said screen grid to said junction comprises a resistor. I 6. A. line deflection circuit 'for a television receiver comprising deflection coil means, an electron discharge device having at least a'cathode, a control grid, a screen grid and an anode, auto-transformer means havingfirst With the values of the table, the Do. flux in the transformer core is reduced by about 25%. A greater reduction could be obtained by the use of deflection coils having higher impedance. V a a The picture shizEt and DC. flux cancellationmay both be increased byreturning the anode of the boost valve V2 to point A; However, in the circuit of FIGURE 2 this is not done since the D.VC. sha'tt obtained would be too large when using the values of the table the British "system. r 7

' and second inductively coupled windings, a source of operating voltage having first and second terminals, first and second capacitor means; a series circuit of said first capacitor, said second windingysaid second capacitor,

and said first winding connected in that order between 1 said first terminal and said anode, means connecting said second terminal to said cathode, means connecting said deflection coil means in parallel with said second \vindin'g and'first capacitor, whereby the voltage at the junction of said first capacitor and second Winding has a direct component and a component that varies at the a frequency of line scanning of said receiver, diode means electron discharge device havinga screen grid and an anode, a source of voltage, output transformer means having first and second inductively coupled windings, means connecting said anode tosaid first Winding, means connecting said first winding to one end or said second Winding, va capacitor connected between said source and the other end of said second winding, means connectsaid deflection coil in parallel with saidsecond winding ponent and an alternating component, and means for con- 2. A line deflection for a television receiver comprising deflection'coi-l means,an output transformer" having winding means, a multigrid electron discharge deconnecting said anode to said winding means fon'produchavinga cathode connected to said'first winding and an anode connected toa point of constant potential, and

means connecting said junction to said sc'reengrid Wherej by the voltage at said screen'grid is higher at the'ends of line scan than in thecenter'of the. linescan in said receiver 7 and screen grid current of said device flows through said deflection coil means.

' if The =circuitof claim 6, in which theanodelof said 7 diode means is connected to said first terminal;

1 and capacitor, whereby avoltage appears at the junction of 1 said capacitor and second-winding that has a direct com fvice having at least an anodeand a, screen griddmans 1 7 8. A line deflection circuit for a cathode ray tube comprising'deflection coil means, an output transformer having first and second inductively coupled windings, a liflsource ofioperating voltage, a multigrid electron discharge tube having at least an anode, a screen grid, and :a controlgrid, input means for supplying an alternating voltage to said control grid of a given line scan fre- "quency, first ,capacitance means connected between one f end of said second winding and said source of operating p,

potential, means connecting said deflection coil means between said source ofoperating potential and the other end of said second winding, second capacitance means connected between said other end of said second winding and an end of said first winding, means connecting said anode to said first Winding for producing a sawtooth 1 current in said deflection coil means, whereby a voltage appears at the junction of said first capacitance means and second winding that has a direct component and an alternating component of the same frequency as said line scan frequency, and means for connecting said screen grid to said junction so that at least a portion of said direct and alternating components of voltage appear at said screen grid whereby the voltage at said screen grid "is higher at the ends of the line scan of said cathode ray tube than at the center of the line scan.

9. Apparatus as defined in claim 8 wherein said means for connecting the screen grid to said junction and said second winding provide a path for screen grid current to flow through said deflection coil rneans.

References Cited in the file of this patent UNITED STATES PATENTS Reker et al. Dec. 20, 1960 

1. A DEFLECTION CIRCUIT FOR PRODUCING A SAWTOOTH WAVEFORM CURRENT IN A DEFLECTION COIL, COMPRISING A MULTIGRID ELECTRON DISCHARGE DEVICE HAVING A SCREEN GRID AND AN ANODE, A SOURCE OF OPERATING VOLTAGE, OUTPUT TRANSFORMER MEANS HAVING FIRST AND SECOND INDUCTIVELY COUPLED WINDINGS, MEANS CONNECTING SAID ANODE TO SAID FIRST WINDING, MEANS CONNECTING SAID FIRST WINDING TO ONE END OF SAID SECOND WINDING, A CAPACITOR CONNECTED BETWEEN SAID SOURCE AND THE OTHER END OF SAID SECOND WINDING, MEANS CONNECTSAID DEFLECTION COIL IN PARALLEL WITH SAID SECOND WINDING AND CAPACITOR, WHEREBY A VOLTAGE APPEARS AT THE JUNCTION OF SAID CAPACITOR AND SECOND WINDING THAT HAS A DIRECT COMPONENT AND AN ALTERNATING COMPONENT, AND MEANS FOR CONNECTING SAID SCREEN GRID TO SAID JUNCTION WHEREBY AT LEAST A PORTION OF SAID DIRECT AND ALTERNATING COMPONENTS APPEAR AT SAID SCREEN GRID AND SCREEN GRID CURRENT FLOWS THROUGH SAID DEFLECTION COIL. 